Clamp for flexible printing plate



July 2l, 1964 F. w. DE TQMBEUR 3,141,405

CLAMP FOR FLEXIBLE PRINTING PLATE Filed Oct. 9, 1961 2 Sheets-Sheet 1 F.W. DE TOMBEUR CLAMP FOR FLEXIBLE PRINTING PLATE July 21, 1964 2Sheets-Sheet 2 Filed Oct. 9, 1961 I IIIHHIIIIIIIOIIUIIIUHIII I Jl. IIII151.3312 172.1...

INVENTOR. fif'oW/z/f M apra/v550@ United States Patent O F 3,141,405CLAMP FOR FLEXIBLE PRINTING PLATE Frederick W. De Tembeur, PomptonLakes, NJ., assignOr to Champlain Company, Inc., Roseland, NJ., acorporation 'uf New York Filed st. 9, 1961, Ser. No. 143,768 11 Claims.(Cl. 10i- 378) This invention relates to printing, and more particularlyto rotary printing presses using flexible printing plates.

Flexible printing plates, usually made of rubber, are secured around therigid cylinder of a printing press. In one form the rubber plate ismounted by means of an adhesive. In another it is secured to a rigidback, which in turn is secured to the cylinder. In still anotherarrangement the rubber plate is secured to a thin strong film made, forexample, of Mylar, and excess film is passed through a slit in thecylinder and pulled tight by means of eccentric shafts located insidethe cylinder. In another form the rubber plate is secured to arelatively thin exible metal back which is somewhat longer than theplate in axial direction, and the protruding metal edges are secured tothe cylinder by releasable bands applied around the cylinder.

The primary object of the present invention is to generally improve theclamps used with such printing plates, particularly exographic printingplates in which the rubber is secured to an exceedingly thin sheet metalback.

The printing cylinder commonly receives two plates, each occupying halfthe cylinder. It is important to be able to change the plates quickly,because with modern high speed operation a large quantity is run off ina short time, following which the plates must be changed, and if thiscannot be done quickly the down time of the printing press will beexcessive. It is also desirable to make the changeover a one manoperation. These things have not been feasible with the flexiblering-like clamps heretofore used.

In accordance with features and objects of the present invention, thereare four separate rigid clamps for a cylinder, each clamp being asemicircular ring of heavy crosssection, preferably received in thestepped end of the cylinder, and having a thin semi-cylindrical lipdimensioned to be received over one end of the metal backing 0f theprinting plate. A clamping screw is disposed radialy, preferably withits head received Within the body of the ring so that there is no radialprojection. By using a ring which is slightly undersize relative to thecylinder and plate, the ends of the ring exert a radial pressure evenwhen using only a single radial screw at the middle of the clamp. Thissingle screw and clamp need not be removed. They are merely loosened,and the clamp is slid axially.

A further object of the invention is to prevent complete removal of theclamp, and for this purpose retainers are provided to limit the slidingmovement of the clamp to an amount which brings the lip of the clamp olfthe plate, thereby releasing the plate.

With flexible printing plates of the character described, theunsupported axially-directed edges of the plate extending between theclamps may tend to lift slightly from the cylinder. A further object ofthe invention is to provide a clamp which tends to stretch or draw theplate taut in axial direction at the said free edges. For this purposethe ring has an inward radial bead near its outer edge, such that whentightened, the clamp screw causes ends of the clamp to move axiallyoutward, thereby tensioning the edges of the printing plate.

To accomplish the foregoing objects, and other more specific objectswhich will hereinafter appear, my invention resides in the clampelements and their relation one to another, and to the printing platesand cylinder, as are hereinafter more particularly described in thefollowing 3,l4l,405 Patented July 21, 1964 ICC specilcation. Thespecification is accompanied by drawings in which:

FIG. 1 shows a printing cylinder equipped with clamps embodying featuresof my invention;

FIG. 2 is an end view of the same;

FIG. 3 is a fragmentary section explanatory of the action of theretainers;

FIG. 4 is a similar section, but taken at a clamp screw instead at aretainer;

FIG. 5 is a section like FIG. 4, but showing the clamp moved intooperative position; and

FIG. 6 shows how the clamp draws the edges of the printing plate taut inaxial direction.

Referring to the drawing, and more particularly to FIG. 1, the printingcylinder 12 has stepped ends indicated at 14. There are four clamps, twoat each end, as shown at 16 and 18 in FIG. 2. Each clamp is asemicircular ring of heavy cross-section, fitting over the stepped end14 of the cylinder, and mostly received in the step. The section isindicated at 20 in FIG. 3, the metal being solid except at the clampingand retainer screws. Each clamp has a thin semicylindrical lip 22dimensioned to be received over one end of the metal backing 24 of therubber printing plate 26, the parts 24 and 26 being shown. in brokenlines.

Retainers 30 limit the axial sliding movement of the clamp to an amountwhich brings the lip 22 off the backing 24 in order to release theplate. This retracted position is shown in FIG. 3. The retainers as hereillustrated are screws which are shouldered at 32 and headed at 34. Thescrews are permanently secured in position, and in normal use need notbe loosened or handled by the operator. They are disposed in axialdirection, and act to hold the clamps in assembled relation with thecylinder, and thus simplify use of the same.

Referring to FIG. 2 the clamps are tightened by means of clamping screws36 which are disposed radially. The head 38 is preferably receivedwithin the body of the ring. In the present case the screw is a sockethead cap screw, and the otherwise solid ring is cut away at 40 toreceive and enclose the head of the screw. This prevents removal or lossof the screw, and lets it serve also to raise the ring, as shown in FIG.4.

Referring to FIG. 4 the bottom wall beneathV the cavity 40 is slotted asshown at 42 to receive the shank of screw 36. The wall 44 of the ringoutside the cavity 40 has an opening 46 affording access to the sockethead 38 of the screw.V FIG. 5 shows how the opening 46 is aligned withthe head 38 of the screw when the clamp has been slid axially intoclamping position, that is, when the lip 22 is over the edge 24 of themetal backing of printing plate 26. The head 38 is larger in diameterthan the hole 46.

Reverting to FIG. 2 the clamps 16 and 18 are preferably made out of asingle accurately machined circular body. This is given a diameterslightly smaller than the diameter of the plate as secured around thecylinder. The difference may be slight, say only 0.005 of an inch. Whenthe two halves are cut apart by means of a diametrical cut, there is anadditional loss of metal because of the Width of the cut, and thisprovides clearance for the clamping action. A single clamping screw 36may be used because the ends of the undersized ring exert a radialpressure as the screw 36 is tightened. It is primarily for this reasonthat the clamp is made of heavy cross section, and any slightdeformation of the ring is well within its elastic limit, so that itretains its shape and dimension even though repeatedly used. Y

It will be understood that the holes in the clamp which receive theretainer screws 30 are made slightly oversized in order to accommodatethe radial motion attendant upon the release or tightening of the clamp.As viewed in FIG. 2 with the clamp screws y36 disposed horizontally theclamp movement is horizontal, and the holes for the retainers have beenwidened or made slot-like in horizontal direction, as shown at 48. Theseslots readily accommodate even a somewhat extensive release movement ofthe clamps.

A further feature of the clamp is the provision of means to tension thefree or axially directed edges of the printing plate. In FIGS. 3, 4 and5 it will be seen that the clamped ring has an inwardly, radiallydirected bead or so-called heel 50 near its outer edge. When the clampscrew 36 is tightened, the clamp ring first is moved downward as shownin FIG. 5, until the heel 50 engages the reduced diameter portion 14 ofthe printing cylinder. As the clamping screw is further tightened, theclamp ring is tilted somewhat, as shown by the change from the brokenline position 22 to the solid line position 22 in FIG. 6. This motion atthe free ends of the clamp draws the corresponding free edge of theprinting plate taut, so that there is no tendency to leave the surfaceof the printing cylinder. The amount of this tilt of the clamp has beenexaggerated in FIG. 6 for clarity, but even a slight motion is highlyeffective for the intended purpose.

To facilitate locating the printing plate on the cylinder, the cylindermay be provided with locating pins indicated at 52, and the printingplates have mating holes. I'he pins and holes are usually centered,relative to the clamp and plate. The operation then is simple andexpeditious. The operator inserts a T or L shaped wrench through thehole 46 into the socket head of the clamping screw, and loosens thesame. On loosening the clamp at each end, they are readily moved back,the printing plate removed, and another applied. The plate is properlylocated by the pilot pins 52. The clamps are then slid back over theends of the plate, and the clamping screw at each end is tightened. Ifboth plates are to be changed the cylinder is turned a half revolution,and the same operation is repeated for the opposite side of thecylinder.

The head of the clamping screw is conned, and therefore it cannot beexcessively loosened or lost. Moreover, the clamping screw serves alsoto release the ring by forcing it outward despite its tight fit on thecylinder. The retainer screws need not be touched, and remainpermanently in position (unless the machine is being disassembled forservicing or repeair). The clamp itself is held against removal or loss.

Reverting to FIG. 1, the printing cylinder may be conventional, and maybe mounted and driven in conventional fashion. In the present case thebearing and bearing housing at one end is suggested in broken lines at60. The corresponding bearing at the other end has been omitted, but thedriving gear for the printing cylinder is shown at 62. This is securedto a hub portion 64 which is keyed to the printing cylinder at 66, androtative adjustment may be provided by means of screws 68 received inarcuate slots.

It is believed that the construction and method of use of my improvedclamp for mounting flexible printing plates on a printing cylinder, aswell as the advantages thereof, will be apparent from the foregoingdetailed description. The printing cylinder commonly receives twoplates, as here illustrated. However, the present invention may also beused with a single printing plate occupying the complete circumferenceof the cylinder, or with more than two printing plates, each occupyingonly a portion of the periphery of the cylinder. It will therefore beapparent that while I have shown and described the invention in apreferred form, changes may be made without departing from the scope ofthe invention, as sought to be defined in the following claims. In theclaims the term semi circular is used for convenience, although theclamp pieces are very nearly but not quite a full semi circle in length.

I claim:

1. lA clamp for mounting a exible printing plate on a printing cylinderhaving stepped ends, said clamp being a semicircular ring of heavysection fitting in the stepped end of the cylinder and having a thinsemicylindrical lip dimensioned to be received over one end of theprinting plate, retainers to limit sliding movement of the clamp inaxial direction to an amount which brings :the lip off the plate inorder to release the plate, a clamping screw disposed radially with itshead within the body of the ring, said ring having an opening for theclamping screw affording the aforesaid axial sliding of the clamprelative to the clamping screw after loosening but without removal ofthe clamping screw, there being four such clamps for a printing cylinderintended to receive two printing plates.

2. In combination, a printing cylinder having stepped ends, two flexibleprinting plates, and four clamps for mounting said flexible printingplates on said printing cylinder, each clamp being a semicircular ringof heavy section fitting in the stepped end of the cylinder and having athin semicylindrical lip received over one end of a printing plate, aclamping screw disposed radially with its head within the body of thering, said screw being located about midway between the ends of thering, said ring having an opening affording access to the head of theclamping screw, said ring having a diameter slightly smaller than thatof the cylinder and plate so that the ends of the ring exert a radialpressure when using only the aforesaid single radial clamp screw at themiddle of the clamp, the said four clamps holding the said two printingplates on said cylinder.

3. A clamp for mounting a flexible printing plate on a printing cylinderhaving stepped ends, said clamp being a semicircular ring of heavysection fitting in the stepped end of the cylinder and having a thinsemicylindrical lip dimensioned to be received over one end of theprinting plate, retainers to limit sliding movement of the clamp inaxial direction to an amount which brings the lip olf the plate in orderto release the plate, a clamping screw disposed radially with its headwithin the body of the ring, said ring having an opening for theclamping screw affording the aforesaid axial sliding of the clamprelative to the clamping screw after loosening but without removal ofthe clamping screw, said ring having a diameter slightly smaller thanthat of the cylinder and plate so that the ends of the ring exert aradial pressure when using only a single radial clamp screw at themiddle of the clamp, there being four such clamps for a printingcylinder intended to receive two printing plates.

4. A clamp for mounting a flexible printing plate on a printing cylinderhaving stepped ends, said clamp being a semicircular ring of heavysection tting in the stepped end of the cylinder and having a thinsemicylindrical lip dimensioned to be received over one end of theprinting plate, a clamping screw disposed radially with its head withinthe body of the ring, said ring having an opening affording access tothe head of the clamping screw, said ring having an inward radial beadnear its outer edge such that the aforesaid clamp screw causes the endsof the clamp to move axially outward to stretch the axially directededges of the printing plate, there being four such clamps for a printingcylinder intended to receive two printing plates.

5. A clamp for mounting a flexible printing plate on a printing cylinderhaving stepped ends, said clamp being a semicircular ring of heavysection fitting in the stepped end of the cylinder and having a thinsemicylindrical lip dimensioned to be received over one end of theprinting plate, retainers to limit sliding movement of the clamp inaxial direction to an amount which brings the lip otf the plate in orderto release the plate, a clamping screw disposed radially with its headwithin the body of the ring, said ring having an opening affordingaccess to the head of the clamping screw, said ring having an inwardradial bead near its outer edge. such that the aforesaid clamp screwcauses the ends of the clamp to move axially outward to stretch theaxially directed edges of the printingy plate, there being four suchclamps for a printing cylinder intended to receive two printing plates.

6. A clamp for mounting a flexible printing plate on a printing cylinderhaving stepped ends, said clamp being a semicircular ring of heavysection tting in the stepped end of the cylinder and having a thinsemicylindrical lip dimensioned to be received over one end of theprinting plate, a clamping screw disposed radially with its head withinthe body of the ring, said ring having an opening alfording access tothe head of the clamping screw, said ring having a diameter slightlysmaller than that of the cylinder and plate so that the ends of the ringexert a radial pressure when using only a single radial clamp screw atthe middle of the clamp, and said ring having an inward radial bead nearits outer edge such that the aforesaid clamp screw causes the ends ofthe clamp to` move axially outward to stretch the axially directed edgesof the printing plate, there being four such clamps for a printingcylinder intended to receive two printing plates.

7. A clamp for mounting a flexible printing plate on a printing cylinderhaving stepped ends, said clamp being a semicircular ring of heavysection tting in the stepped end of the cylinder and having a thinsemicylindrical lip dimensioned to be received over one end of theprinting plate, retainers to limit sliding movement of the clamp inaxial direction to an amount which brings the lip off the plate in orderto release the plate, a clamping screw disposed radially with its headwithin the body of the ring, said ring having an opening afording accessto the head of the clamping screw, said ring having a diameter slightlysmaller than that of the cylinder and plate so that the ends of the ringexert a radial pressure when using only a single radial clamp screw atthe middle of the clamp, and said ring having an inward radial bead nearits outer edge such that the aforesaid clamp screw causes the ends ofthe clamp to move axially outward to stretch the axially directed edgesof the printing plate, there being four such clamps for a printingcylinder intended to receive two printing plates.

8. In combination, a printing cylinder, two ilexible printing plates andfour clamps for mounting said flexible printing plates on said printingcylinder, each clamp comprising an arcuate ring of heavy section havinga thin arcuate lip dimensioned to be received over one end of theprinting plate, said ring being about a half circle long, and a clampingscrew disposed radially about midway between the ends of .the ring, saidring having a diameter slightly smaller than that of the cylinder andplate so that the ends of the arcuate ring exert a radial pressure whenusing only a single radial clamp screw at the middle of the clamp.

9. A clamp for mounting a flexible printing plate on a printingcylinder, said clamp comprising an arcuate ring of heavy section havinga thin arcuate lip dimensioned to be received over one end of theprinting plate, retainers to limit sliding movement of the clamp inaxial direction to an amount which brings the lip ot the plate in orderto release the plate, and a clamping screw disposed radially, said ringhaving an opening for the clamping screw affording the aforesaid axialmovement of the clamping screw after loosening but without removal ofthe clamping screw.

l0. In combination, a printing cylinder, two exible printing plates andfour clamps for mounting said exible printing plates on said printingcylinder, each clamp comprising an arcuate ring of heavy section havinga thin arcuate lip dimensioned to be received over one end of theprinting plate, said ring being about a half circle long, retainers tolimit sliding movement of the clamp in axial direction to an amountwhich brings the lip off the plate in order to release the plate, and aclamping screw disposed radially about midway between the ends of thering, said ring having a diameter slightly smaller than that of thecylinder and plate so that the ends of the arcuate ring exert a radialpressure when using only a single radial clamp screw at the middle ofthe clamp.

1l. A clamp for mounting a flexible printing plate on a printingcylinder, said clamp comprising an arcuate ring of heavy section havinga thin arcuate lip dimensioned to be received over one end of theprinting plate, retainers to limit sliding movement of the clamp inaxial direction to an amount which brings the lip off the plate in orderto release the plate, and a clamping screw disposed radially, said ringhaving a diameter slightly smaller than that of the cylinder and plateso that the ends of the ring exert a radial pressure when using only asingle radial clamp screw at the middle of the clamp, said ring havingan inward radial bead near its outer edge such that the aforesaid'sclamp screw causes the ends of the clamp to move axially outward tostretch the axially directed edges of the printing plate.

References Cited in the le of this patent UNITED STATES PATENTS1,421,982 Nordfors July 4, 1922 1,856,162 Isbell May 3, 1932 2,984,954Burt May 23, 1961

7. A CLAMP FOR MOUNTING A FLEXIBLE PRINTING PLATE ON A PRINTING CLYINDERHAVING STEPPED ENDS, SAID CLAMP BEING A SEMICIRCULAR RING OF HEAVYSECTION FITTING IN THE STEPPED END OF THE CYLINDER AND HAVING A THINSEMICYLINDRICAL LIP DIMENSIONED TO BE RECEIVED OVER ONE END OF THEPRINTING PLATE, RETAINERS TO LIMIT SLIDING MOVEMENT OF THE CLAMP INAXIAL DIRECTION TO AN AMOUNT WHICH BRINGS THE LIP OFF THE PLATE IN ORDERTO RELEASE THE PLATE, A CLAMPING SCREW DISPOSED RADIALLY WITH ITS HEADWITHIN THE BODY OF THE RING, SAID RING HAVING AN OPENING AFFORDINGACCESS TO THE HEAD OF THE CLAMPING SCREW, SAID RING HAVING A DIAMETERSLIGHTLY SMALLER THAN THAT OF THE CYLINDER AND PLATE SO THAT THE ENDS OFTHE RING EXERT A RADIAL PRESSURE WHEN USING ONLY A SINGLE RADIAL CLAMPSCREW AT THE MIDDLE OF THE CLAMP, AND SAID RING HAVING AN INWARD RADIALBEAD NEAR ITS OUTER EDGE SUCH THAT THE AFORESAID CLAMP SCREW CAUSES THEENDS OF THE CLAMP TO MOVE AXIALLY OUTWARD TO STRETCH THE AXIALLYDIRECTED EDGES OF THE PRINTING PLATE, THERE BEING FOUR SUCH CLAMPS FOR APRINTING CYLINDER INTENDED TO RECEIVE TWO PRINTING PLATES.